In recent years, wireless communication systems represented by IEEE802.11a/b/g are achieving widespread use. These are called wireless LAN (local area network) systems, which are communication systems supporting a system equivalent to Ethernet (registered trademark) used in a wired LAN system.
A wireless LAN system at first was used such as for a portable or mobile personal computer and mobile wireless terminal. After that, it became used in various fields. For example, to eliminate complicatedness of wiring cables, a wireless LAN system is used for a terminal with its service space fixed. Conventionally, such application examples include a case where a wireless LAN system is used for distribution service of content such as audio and video in an aircraft (refer to literature 1 for example).
In this example, a wireless LAN system is incorporated in an aircraft; content data is sent out to a wireless terminal placed at each passenger seat, which implements information distribution service using a wireless LAN system.
The distribution system includes a server of the system for accumulating content data for presenting to passengers; and plural wireless access points (referred to as “access point” hereinafter), which are wireless base stations connected to the server, placed in the aircraft. Further, a wireless terminal is placed at each seat, and each access point is positioned so that one access point covers plural wireless terminals.
To position an access point, the cabin space is divided into plural small areas, and one access point is made correspond to one small area. Then, each access point is placed at an appropriate position and each channel is allocated so as to cover the entire service area of the cabin space.
To avoid interference between each wireless terminal, a directional antenna is arranged so as to radiate radio waves with a minimum of interference and disturbance made to a small area outside the own area. Then, setting is made so that wireless communications are performed with each wireless terminal inside the own area using a predetermined channel. Further, arrangement is made so that one access point communicates with each wireless terminal inside the small area where the access point is placed by time-dividing the frequency band of a channel used for wireless communications. This structure allows one channel to perform information distribution service individually for plural wireless terminals.
Conventionally, as a display means of the information distribution service, an image display device (abbreviated as “monitor” hereinafter) equipped on the back side of each seat is used.
In recent years, however, to enhance further convenience and comfort for passengers, a portable monitor (a monitor with wireless connection added) is receiving attention. When performing wireless communications in an aircraft by a conventional method, if a portable monitor moves beyond the cover area of an access point that has been used, the communication efficiency decreases and interference with other terminal devices occurs undesirably.
Conventionally, to present content such as audio and video (abbreviated as “AV information” hereinafter) in an aircraft, audio information is presented from the seat where the user is seated and video information is presented from the display device placed on the seat one row ahead of the seat where the user is seated. As the system configuration, an SEB (seat electronics box) for separating AV information received into audio and video information is arranged at each seat, and audio feedback method (seats adjacent to an SEB lengthwise are connected to each other using underfloor wiring) is used.
To receive AV information service with a portable monitor detached from the seat, however, audio feedback method cannot be used. Particularly, one to one relation between a monitor and a seat does not hold, and thus individual in-flight information service presented to each seat cannot be received by the monitor, or audio conforming to the video cannot be received at the own seat. Further, operation related to in-flight service (e.g. CA call (operation for calling a cabin attendant), lighting) is affected.
[Patent literature 1] Japanese Translation of PCT Publication No. 2006-506899